Conjugated diene/monovinylarene block copolymers, methods for preparing same, and polymer blends

ABSTRACT

A block copolymer comprising at least three consecutive conjugated diene/monovinylarene tapered blocks is provided. Other aspects of this invention include a polymerization process for preparing the block copolymer and polymer blends comprising the block copolymer. The block copolymer and polymer blends exhibit excellent optical and mechanical properties.

This invention relates to conjugated diene/monovinylarene blockcopolymers, methods of preparing same and polymer blends comprising suchcopolymers.

BACKGROUND

Copolymers of conjugated diene/monovinylarene are known and useful for avariety of purposes. Of particular interest are polymers that can beformed into colorless, transparent articles having good physicalproperties, such as impact resistance. Such articles are useful in toys,window pieces, beverage containers, and packaging such as blisterpackaging.

The polymers should also exhibit sufficient thermal stability to besuitable for use with conventional injection molding equipment. For manyapplications copolymer blends containing high amounts of styrene arerequired. Such polymers are generally prepared by blending certainmonovinylarene-conjugated diene copolymers with styrene polymers.However such blends often contain an undesirable haze and bluecoloration. It would therefore be desirable to develop polymers andpolymer blends having a combination of low blueness, good clarity,hardness, stiffness, and toughness.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a polymer useful forpreparing blends having good optical clarity.

It is another object of this invention to provide a polymer useful forpreparing blends having low blueness.

It is another object of this invention to provide a process forpreparing such polymers having good optical and mechanical properties.

In accordance with this invention a block copolymer comprising at leastthree consecutive conjugated diene/monovinylarene tapered blocks isprovided. As used herein, consecutive means three sequential taperedblocks with no intervening homopolymer blocks. The tapered blockscontain a mixture of monovinylarene and conjugated diene.

In accordance with other aspects of this invention, a polymerizationprocess for preparing the block copolymer and polymer blends comprisingthe block copolymer are provided.

DETAILED DESCRIPTION OF THE INVENTION

The basic starting materials and polymerization conditions for preparingconjugated diene/monovinylarene block copolymer are disclosed in U.S.Pat. Nos. 4,091,053; 4,584,346; 4,704,434; 4,704,435; and 5,227,419; thedisclosures of which are hereby incorporated by reference.

Suitable conjugated dienes which can be used in the block copolymersinclude those having 4 to 12 carbon atoms per molecule, with thosehaving 4 to 8 carbon atoms preferred. Examples of such suitablecompounds include 1,3-butadiene, 2-methyl-1,3-butadiene,2-ethyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene,3-butyl-1,3-octadiene, and mixtures thereof. The preferred dienes are1,3-butadiene and isoprene, more preferably 1,3-butadiene.

Suitable monovinylarene compounds which can be used in the blockcopolymers include those having 8 to 18 carbon atoms per molecule,preferably 8 to 12 carbon atoms. Examples of such suitable compoundsinclude styrene, alpha-methylstyrene, 2-methylstyrene, 3-methylstyrene,4-methylstyrene, 2-ethylstyrene, 3-ethylstyrene, 4-ethylstyrene,4-n-propylstyrene, 4-t-butylstyrene, 2,4-dimethylstyrene,4-cyclohexylstyrene, 4-decylstyrene, 2-ethyl-4-benzylstyrene,4-(4-phenyl-n-butyl)styrene, 1-vinylnaphthalene, 2-vinylnaphthalene, andmixtures thereof. Styrene is the preferred monovinylarene compound.

The relative amount of conjugated diene and monovinylarene in the blockcopolymer can vary broadly depending on the particular characteristicsdesired. Generally, the conjugated diene/monovinylarene block copolymerwill contain monovinylarene monomer in an amount in the range of fromabout 55 weight percent to about 95 weight percent based on the totalweight of the final block copolymer, preferably in the range of fromabout 60 weight percent to about 95 weight percent, and more preferablyin the range of from 65 weight percent to 90 weight percent.

Generally the conjugated diene monomer will be present in the finalblock copolymer in an amount in the range of from about 45 weightpercent to about 5 weight percent based on the total weight of the finalblock copolymer, preferably in the range of from about 40 weight percentto about 5 weight percent, and more preferably in the range of from 35weight percent to 10 weight percent.

The inventive polymer contains at least three consecutive conjugateddiene/monovinylarene tapered blocks, which are incorporated sequentiallyinto the block copolymer with no intervening homopolymer blocks.

The amount of each monomer in the tapered block can vary broadlydepending on the particular characteristics desired. Generallymonovinylarene will be present in each tapered block in an amount in therange of from about one weight percent to about 20 weight percent basedon the total weight of the final block copolymer, preferably from about2 weight percent to about 15 weight percent.

Generally the conjugated diene will be present in each tapered block inan amount in the range of from about one weight percent to about 15weight percent based on the total weight of the final block copolymer,preferably from about 2 weight percent to about 12 weight percent. It isespecially preferred that all conjugated diene monomer present in thefinal block copolymer be incorporated into the tapered blocks.

The relative amount of each monomer in the tapered block can also varybroadly depending on the particular characteristics desired. Generallythe conjugated diene will be present in each tapered block in an amountin the range of from about 0.1 parts to about 10 parts per partmonovinylarene in the tapered block, preferably from about 0.2 parts toabout 5 parts per part monovinylarene.

The monomer and monomer mixtures are copolymerized sequentially in thepresence of an initiator. The initiators can be any of theorganomonoalkali metal compounds known for such purposes. Preferablyemployed are compounds of the formula RM, wherein R is an alkyl,cycloalkyl, or aryl radical containing 4 to 8 carbon atoms, morepreferably R is an alkyl radical. M is an alkali metal, preferablylithium. The presently preferred initiator is n-butyl lithium.

The amount of initiator employed depends upon the desired polymer orincremental block molecular weight, as is known in the art, and isreadily determinable, making due allowance for traces of poisons in thefeed streams. Generally the initiator will be present in an amount inthe range of from about 0.01 phm (parts by weight per hundred parts byweight of total monomer) to about 1.0 phm, preferably about 0.01 phm toabout 0.5 phm, and more preferably from 0.01 phm to 0.2 phm.

Small amounts of polar organic compounds, such as ethers, thioethers,and tertiary amines can be employed in the hydrocarbon diluent toimprove the effectiveness of the initiator and to randomize at leastpart of the monovinylarene monomer in a mixed monomer charge.Tetrahydrofuran is currently preferred. When employed, the polar organiccompound is present in an amount sufficient to improve the effectivenessof the initiator. For example, when employing tetrahydrofuran to improvethe effectiveness of the initiator, the tetrahydrofuran is generallypresent in an amount in the range of from about 0.01 to about 1.0 phm,preferably from about 0.02 to about 1.0 phm.5

The polymerization process is carried out in a hydrocarbon diluent atany suitable temperature in the range of from about -100° C. to about150° C., preferably from 0° to 150° C., at pressures sufficient tomaintain the reaction mixture substantially in the liquid phase.Preferred hydrocarbon diluents include linear or cycloparaffins ormixtures thereof. Typical examples include pentane, hexane, octane,cyclopentane, cyclohexane, and mixtures thereof. Cyclohexane ispresently preferred. The polymerization is carried out in a substantialabsence of oxygen and water, preferably under an inert gas atmosphere.

Each monomer charge or monomer mixture charge is polymerized undersolution polymerization conditions such that the polymerization of eachmonomer charge or monomer mixture charge is substantially completebefore charging a subsequent charge.

Typical initiator, monomer and monomer mixture charge sequences include,but are not limited to the following:

Mode A

(a) monovinylarene monomer and initiator,

(b) monovinylarene monomer and initiator,

(c) conjugated diene/monovinylarene monomer mixture,

(d) conjugated diene/monovinylarene monomer mixture,

(e) conjugated diene/monovinylarene monomer mixture, and

(f) coupling agent;

Mode B

(a) monovinylarene monomer and initiator,

(b) monovinylarene monomer and initiator,

(c) conjugated diene/monovinylarene monomer mixture,

(d) conjugated diene/monovinylarene monomer mixture,

(e) conjugated diene/monovinylarene monomer mixture,

(f) conjugated diene/monovinylarene monomer mixture, and

(g) coupling agent;

Mode C

(a) monovinylarene monomer and initiator,

(b) monovinylarene monomer and initiator,

(c) conjugated diene/monovinylarene monomer mixture,

(d) conjugated diene/monovinylarene monomer mixture,

(e) conjugated diene/monovinylarene monomer mixture,

(f) conjugated diene/monovinylarene monomer mixture,

(g) conjugated diene/monovinylarene monomer mixture, and

(h) coupling agent.

Mode D

(a) monovinylarene monomer and initiator,

(b) conjugated diene/monovinylarene monomer mixture and initiator,

(c) conjugated diene/monovinylarene monomer mixture,

(d) conjugated diene/monovinylarene monomer mixture, and

(e) coupling agent;

Mode E

(a) monovinylarene monomer and initiator,

(b) conjugated diene/monovinylarene monomer mixture and initiator,

(c) conjugated diene/monovinylarene monomer mixture,

(d) conjugated diene/monovinylarene monomer mixture,

(e) conjugated diene/monovinylarene monomer mixture, and

(f) coupling agent;

Mode F

(a) monovinylarene monomer and initiator,

(b) conjugated diene/monovinylarene monomer mixture and initiator,

(c) conjugated diene/monovinylarene monomer mixture,

(d) conjugated diene/monovinylarene monomer mixture,

(e) conjugated diene/monovinylarene monomer mixture,

(f) conjugated diene/monovinylarene monomer mixture, and

(g) coupling agent.

The monomer mixture can be premixed and charged as a mixture or themonomers can be charged simultaneously. In step (a) the initiator can beadded before or after the monovinylarene monomer charge. In large scaleoperations it may be desirable to add the monovinylarene monomer beforeadding the initiator in step (a). In subsequent steps containinginitiator, the initiator should be added prior to the monomer or monomermixture.

Prior to coupling, typical polymer chains prepared by the abovedescribed sequential polymerizations include the following:

Mode A

S₁ -S₂ -B₁ /S₃ -B₂ /S₄ -B₃ /S₅ -Li

S₂ -B₁ /S₃ -B₂ /S₄ -B₃ /S₅ -Li

Mode B

S₁ -S₂ -B₁ /S₃ -B₂ /S₄ -B₃ /S₅ -B₄ /S₆ -Li

S₂ -B₁ /S₃ -B₂ /S₄ -B₃ /S₅ -B₄ /S₆ -Li

Mode C

S₁ -S₂ -B₁ /S₃ -B₂ /S₄ -B₃ /S₅ -B₄ /S₆ -B₅ /S₇ -Li

S₂ -B₁ /S₃ -B₂ /S₄ -B₃ /S₅ -B₄ /S₆ -B₅ /S₇ -Li

Mode D

S₁ -B₁ /S₂ -B₂ /S₃ -B₃ /S₄ -Li

B₁ /S₂ -B₂ /S₃ -B₃ /S₄ -Li

Mode E

S₁ -B₁ /S₂ -B₂ /S₃ -B₃ /S₄ -B₄ /S₅ -Li

B₁ /S₂ -B₂ /S₃ -B₃ /S₄ -B₄ /S₅ -Li

Mode F

S₁ -B₁ /S₂ -B₂ /S₃ -B₃ /S₄ -B₄ 1S₅ -B₅ 1S₆ -Li

B₁ /S₂ -B₂ /S₃ -B₃ /S₄ -B₄ /S₅ -B₅ /S₆ -Li

where S is a monovinylarene block, B/S is a tapered block containing amixture of monovinylarene and conjugated diene, and Li is residue from amonoalkali metal initiator.

The coupling agent is added after polymerization is complete. Suitablecoupling agents include the di- or multivinylarene compounds, di- ormultiepoxides, di- or multiisocyanates, di- or multiimines, di- ormultialdehydes, di- or multiketones, alkoxytin compounds, di- ormultihalides, particularly silicon halides and halosilanes, mono-, di-,or multianhydrides, di-, or multiesters, preferably the esters ofmonoalcohols with polycarboxylic acids, diesters which are esters ofmonohydric alcohols with dicarboxylic acids, diesters which are estersof monobasic acids with polyalcohols such as glycerol, and the like, andmixtures of two or more such compounds.

Useful multifunctional coupling agents include epoxidized vegetable oilssuch as epoxidized soybean oil, epoxidized linseed oil and the like ormixtures thereof. The presently preferred coupling agent is epoxidizedvegetable oil. Presently preferred is epoxidized soybean oil.

Any effective amount of the coupling agent can be employed. While theamount is not believed to be critical, generally a stoichiometric amountrelative to the active polymer alkali metal tends to promote maximumcoupling. However, more or less than stoichiometric amounts can be usedfor varying coupling efficiency where desired for particular products.Typically the total amount of coupling agent employed in thepolymerization is in the range of from about 0.1 phm to about 20 phm,preferably from about 0.1 phm to about 5 phm, and more preferably 0.1phm to 2 phm.

Following completion of the coupling reaction, the polymerizationreaction mixture can be treated with a terminating agent such as water,alcohol, phenols or linear saturated aliphatic mono-dicarboxylic acidsto remove alkali metal from the block copolymer and for color control.The preferred terminating agent is water and carbon dioxide.

The polymer cement (polymer in polymerization solvent) usually containsabout 10 to 40 weight percent solids, more usually 20 to 35 weightpercent solids. The polymer cement can be flashed to evaporate a portionof the solvent so as to increase the solids content to a concentrationof about 50 to about 99 weight percent solids, followed by vacuum ovenor devolatilizing extruder drying to remove the remaining solvent.

The block copolymer can be recovered and worked into the desired shape,such as by milling, extrusion, or injection molding. The block copolymercan also contain additives such as antioxidants, antiblocking agents,release agents, fillers, extenders, and dyes, and the like as long asthe amounts and types do not interfere with the objectives of thisinvention.

In another embodiment of this invention, the block copolymers areblended with other styrenic polymers such as polystyrene,acrylonitrile-butadiene-styrene copolymers, and styrene-acrylonitrilecopolymers.

The styrenic polymers are usually (a) homopolymers of styrene; or (b)copolymers of styrene as a major component with a minor amount of anyother copolymerizable monovinylarene compound other than styrene, suchas alpha-methylstyrene, vinyltoluene or para-tert-butyl styrene. A minoramount of other monomers such as methyl acrylate, methyl methacrylate,acrylonitrile and the like can be copolymerized with the styrene. Blendscomprising the inventive block copolymers and polystyrene exhibit acombination of desirable characteristics and they are preferred.

The styrenic polymers can be prepared by any method known in the art.The styrenic polymers are commonly prepared by heating styrene and anycomonomer at temperatures in the range of 100° C. to 200° C. and underpressure sufficient to polymerize the monomers. The polymerization canalso be carried out at lower temperatures by the addition of freeradical generating peroxide catalysts such as benzoyl peroxide, acetylperoxide, di-t-butyl peroxide and the like. Alternatively, thepolymerization can be carried out in suspension to yield a dry powder orin emulsion, usually resulting in a latex of polystyrene which can becoagulated to yield the solid powdery polystyrene. The polymerizationcan also be carried out in solution with precipitation of the product.Solvent can be removed by standard techniques such as steam stripping orsolvent evaporation.

High impact polystyrene can also be employed in blends with theinventive block copolymers. High impact polystyrenes can be prepared bypolymerizing styrene in the presence of elastomer, typicallypolybutadiene rubber.

The relative amounts of block copolymer and styrenic polymer employed inpreparing the polymer blend can vary broadly depending on the desiredcharacteristics of the final polymer blend. Typical polymer blendscontain block copolymer in an amount in the range of from about 5 weightpercent to about 95 weight percent based on the total weight of thefinal polymer blend, preferably from about 10 weight percent to about 90weight percent, and more preferably from about 20 weight percent toabout 80 weight percent based on the total weight of the final polymerblend.

The styrenic polymer will be present in an amount in the range of fromabout 5 weight percent to about 95 weight percent based on the totalweight of the final polymer blend, preferably from about 10 weightpercent to about 90 weight percent, and more preferably from about 20weight percent to about 80 weight percent based on the total weight ofthe final polymer blend.

The polymer blends described above exhibit a combination of desirablecharacteristics. The polymer blends exhibit haze of less than about 15percent, preferably less than about 10 percent measured according toASTM 1003, using test specimens of 50 mil thickness and an instrumentsuch as a Gardner Hazemeter. When using test specimens of 15 milthickness and an instrument such as a HunterLab ColorQuest, preferablythe haze will be less than 5 percent.

The polymer blends preferably exhibit a Notched Izod Impact Strength ofgreater than about 0.2 ft·lb/inch, preferably greater than 0.3ft·lb/inch measured according to ASTM D-256.

The polymer blends also exhibit low blueness, preferably having anabsolute number for blueness of less than 20, measured with a HunterLabD25 M Optical Sensor using three stacked injection molded (350° F./30tons/2 minutes) resin disks of 50 mil thickness measured against acalibrated black background. Positive numbers represent yellow andnegative numbers represent blue. When employing 15 mil thick extrudedsheet (400 ° F./20 mil nominal die gap), the absolute number forblueness will preferably be less than 15.

Blending can be accomplished by any method known in the art includingmelt blending and solution blending. Preferably the polymers are meltblended employing any desired means such as a Banbury mixer, a hot roll,or an extruder. More preferably the polymers are melt blended employingextruder blending techniques. Single or twin screw extruders can beutilized. The polymers and any other ingredients or additives can be dryblended prior to the melt blending.

The blending conditions depend upon the blending technique and polymersemployed. If an initial dry blending of the polymer is employed, the dryblending conditions may include temperatures from room temperature up tojust under the melting temperature of the polymer, and blending times inthe range of a few seconds to hours, e.g. 2 seconds to 30 minutes.

During the melt blending, the temperature at which the polymers arecombined in the blender will generally be in the range between thehighest melting point of the polymers employed and up to about 100ICabove such melting point.

The time required for the melt blending can vary broadly and depends onthe method of blending employed. The time required is the timesufficient to thoroughly mix the components. Generally, the individualpolymers are blended for a time of about 10 seconds to about 15 minutes.

The polymer blends can contain additives such as stabilizers,anti-oxidants, anti-blocking agents, mold release agents, dyes,pigments, and flame retardants, as well as fillers and reinforcingagents, such as glass fibers, as long as the amounts and types do notinterfere with the objectives of this invention.

The block copolymers and polymer blends prepared according to theinvention are useful for the production of articles prepared by milling,extrusion, blow molding, or injection molding.

The following examples are presented to further illustrate the inventionand are not meant to limit the scope thereby.

EXAMPLE

The following example demonstrates the preparation of block copolymersand the combination of clarity and mechanical properties of variouspolymer blends.

Styrene/butadiene block copolymer (SB) was prepared employing asequential solution polymerization under nitrogen. Polymerization runswere carried out in a stirred, 100 gallon carbon steel reactor withinternal cooling coils employing essentially anhydrous reactants andconditions.

Lines were flushed with 0.5 kg cyclohexane following each charge.Polymerization was allowed to continue to completion after each monomeror monomer mixture charge. Polymerization temperature ranged from about38° to about 120° C. and pressure ranged from about 2 psig to about 60psig. Total monomer weight was about 90 kg. The sequence of charges oftetrahydrofuran (THF), styrene (S), n-butyllithium initiator (i),butadiene/styrene mixture (B/S), and coupling agent (CA) was as follows.

Block Copolymer A1

0.5 THF, 0.05i₁, 30S₁, 0.05i₂, 20S₂, (5B₁ /10S₃), (10B₂ /10S₄), (10B₃/55₅), CA. (amounts in parts/100 parts monomer)

Block Copolymer A2

0.1 THF, 0.05i₁, 30S₁, 0.05i₂, 20S₂, (5B₁ /10S₃), (10B₂ /10S₄), (10B₃/5S₅), CA. (amounts in parts/100 parts monomer)

Following completion of the sequential polymerizations, Vikoflex 7170,(a coupling agent comprising epoxidized soybean oil sold by VikingChemical Co.) was charged to the reactor. After completion of thecoupling reaction, the reaction was terminated by adding CO₂ and 0.2 phmwater. The styrene/butadiene block copolymers were stabilized with 0.25phr (parts per hundred resin) Irganox 1076 and 1.0 phr tris(nonylphenyl)phosphite.

The block copolymers A1 and A2 exhibited melt flows of 7.2 and 6.5 g/10min. respectively measured according to ASTM D-1238, condition G.

Polystyrene (PS), Novacor 555 GPPS, available from Novacor PlasticsDivision was blended with S/B block copolymer at 60:40 and 50:50 blockcopolymer:polystyrene weight ratios.

The results are summarized in Table 1. Blueness, tristumulus value "b",a measure of blue and yellow color, was measured with a HunterLab D25 MOptical Sensor using 15 mil extruded sheet (400 F.°/20 mil nominal diegap). Measurements were against a calibrated black background. Apositive number represents yellow and a negative number represents blue.

In the following table:

Copolymer is the styrene/butadiene block copolymer employed.

CP/PS is the ratio of block copolymer to polystyrene employed in thepolymer blend.

Haze in percent was measured according to ASTM 1003 on 15 mil sheetsusing a HunterLab ColorQuest instrument.

Blueness was measured as described above.

                  TABLE 1                                                         ______________________________________                                        Blend   Copolymer CP/PS      Haze %                                                                              Blueness                                   ______________________________________                                        101     A1        60/40      2.49  -10.0                                      102     A1        50/50      2.92  -12.2                                      103     A2        60/40      2.53   -9.8                                      104     A2        50/50      2.86  -10.4                                      ______________________________________                                    

The results in Table 1 demonstrate that polymer blends employing a blockcopolymer containing three tapered blocks exhibit a combination of goodclarity and low blueness. The polymer blends also exhibited good impacttoughness and ductility.

That which is claimed is:
 1. A coupled conjugated diene/monovinylareneblock copolymer comprising at least three consecutive conjugateddiene/monovinylarene tapered blocks:wherein the monovinylarene containsfrom 8 to 18 carbon atoms; and wherein the conjugated diene containsfrom 4 to 12 carbon atoms.
 2. A block copolymer according to claim 1wherein the conjugated diene is butadiene.
 3. A block copolymeraccording to claim 2 wherein the monovinylarene is styrene.
 4. A blockcopolymer according to claim 1 wherein the monovinylarene is present inan amount in the range of from about 55 weight percent to about 95weight percent based on the total weight of the final block copolymerand the conjugated diene is present in an amount in the range of fromabout 5 weight percent to about 45 weight percent based on the totalweight of the final block copolymer.
 5. A block copolymer according toclaim 4 wherein the monovinylarene is present in an amount in the rangeof from about 60 weight percent to about 95 weight percent based on thetotal weight of the final block copolymer and the conjugated diene ispresent in an amount in the range of from about 5 weight percent toabout 40 weight percent based on the total weight of the final blockcopolymer.
 6. A block copolymer according to claim 5 wherein themonovinylarene is present in an amount in the range of from about 65weight percent to about 90 weight percent based on the total weight ofthe final block copolymer and the conjugated diene is present in anamount in the range of from about 10 weight percent to about 35 weightpercent based on the total weight of the final block copolymer.
 7. Ablock copolymer according to claim 6 wherein each individual taperedblock contains the monovinylarene in an amount in the range of fromabout one weight percent to about 20 weight percent based on the totalweight of the final block copolymer and the conjugated diene is presentin an amount in the range of from about one weight percent to about 15weight percent based on the total weight of the final block copolymer.8. A block copolymer according to claim 7 wherein each individualtapered block contains the monovinylarene in an amount in the range offrom about one weight percent to about 15 weight percent based on thetotal weight of the final block copolymer and the conjugated diene in anamount in the range of from about one weight percent to about 12 weightpercent based on the total weight of the final block copolymer.
 9. Ablock copolymer according to claim 1 which is prepared by coupling thefollowing polymer chains:S₁ -S₂ -B₁ /S₃ -B₂ /S₄ -B₃ /S₅ -Li S₂ -B₁ /S₃-B₂ /S₄ -B₃ /S₅ -Liwherein S represents monovinylarene blocks, B/Srepresents tapered blocks of conjugated diene/monovinylarene and Li isresidue from a monoalkali metal initiator.